title: The structural basis for MCM2-7 helicase activation by GINS and Cdc45.
abstract: Two central steps for initiating eukaryotic DNA replication involve loading of the Mcm2-7 helicase onto double-stranded DNA and its activation by GINS-Cdc45. To better understand these events, we determined the structures of Mcm2-7 and the CMG complex by using single-particle electron microscopy. Mcm2-7 adopts two conformations--a lock-washer-shaped spiral state and a planar, gapped-ring form--in which Mcm2 and Mcm5 flank a breach in the helicase perimeter. GINS and Cdc45 bridge this gap, forming a topologically closed assembly with a large interior channel; nucleotide binding further seals off the discontinuity between Mcm2 and Mcm5, partitioning the channel into two smaller pores. Together, our data help explain how GINS and Cdc45 activate Mcm2-7, indicate that Mcm2-7 loading may be assisted by a natural predisposition of the hexamer to form open rings, and suggest a mechanism by which the CMG complex assists DNA strand separation.
authors.affiliation: Department of Molecular and Cell Biology, University of California, Berkeley, Berkeley, California, USA.
authors.forename: Alessandro
authors.initials: A
authors.lastname: Costa
authors.forename: Ivar
authors.initials: I
authors.lastname: Ilves
authors.forename: Nele
authors.initials: N
authors.lastname: Tamberg
authors.forename: Tatjana
authors.initials: T
authors.lastname: Petojevic
authors.forename: Eva
authors.initials: E
authors.lastname: Nogales
authors.forename: Michael R
authors.initials: MR
authors.lastname: Botchan
authors.forename: James M
authors.initials: JM
authors.lastname: Berger
mesh_terms: D000818:Animals; D018797:Cell Cycle Proteins / Q000378:metabolism*; D002868:Chromosomal Proteins, Non-Histone / Q000737:chemistry / Q000378:metabolism*; D029721:Drosophila Proteins / Q000737:chemistry / Q000378:metabolism*; D004789:Enzyme Activation; D064110:Minichromosome Maintenance Proteins; D008958:Models, Molecular; D011487:Protein Conformation
chemical_list: C547399:Cdc45 protein, Drosophila; D018797:Cell Cycle Proteins; D002868:Chromosomal Proteins, Non-Histone; D029721:Drosophila Proteins; C555716:MCM2 protein, Drosophila; D064110:Minichromosome Maintenance Proteins